Known are, in this specific field of application, protection apparatus which are intended for installation at consumer's outlets of single-phase or three-phase power supplies of the civil or industrial kinds.
Such prior apparatus include a protective automatic breaker, usually of the magnetothermic type, whose break mechanism is driven by a solenoid.
Also provided is a differential current sensor which comprises a toroidal transformer encircling the power supply line and being adapted to warn of the appearance of such currents, also referred to as leakage currents, by sensing any unbalance in the currents flowing through the line conductors.
The sensor is connected to the solenoid coil so as to trip off the breaker mechanism on a predetermined differential current value being exceeded.
High performance (type "A") protection apparatus, such as those designed to become operative on unidirectional or pulsed currents being sensed, include an electronic circuit connected between the sensor and the solenoid. This circuit is generally made up of series and/or cascade connected capacitors.
While being in many ways advantageous and substantially up to their intended function, such apparatus still have several drawbacks, as pointed out herein below.
The current-detection and break mechanism trip-off steps involve a sequel of energy conversions from electric into electromagnetic, and vice versa, and ultimately into mechanical, which unavoidably brings about losses and restricts the apparatus response.
The provision of an electronic circuit including capacitors is both cost-, space-, and power-intensive.
The solenoid and the toroidal transformer which forms the current sensor, by their very presence restrict the possibility of making such protection apparatus more compact.
Patent Application GB-A-2074380 discloses an electromagnetic breaker having a yoke polarized by a permanent magnet and a movable element which is attracted by the yoke against spring; electric conductors are passed through a hole in the yoke so that the magnetic flux induced by conductors through the yoke interferes with the permanent magnetic flux from the permanent magnet.
The technical problem that underlies this invention is to provide an electromagnetic actuator of the type of a relay, which has such structural and performance characteristics as to overcome the above-noted drawbacks.